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← The ApothecaryRutaceaedried bark (bright yellow inner bark), fruit (Ainu use)Fact-checked 24 October 2026

Amur cork tree

Phellodendron amurense

Also calledHuang bai / huang bo 黄柏 (Chinese) · Guan huang bo (Chinese) · Kihada, ōbaku (Japanese) · Hwangbaek (Korean) · Sikerpe, shikerebe-ni (Ainu) · Amur cork tree, Siberian cork tree

An East Asian tree whose bright yellow, bitter inner bark, huang bai, is one of the main heat-clearing herbs of Chinese medicine. Its chief alkaloid is berberine. WHO found no clinical trials of the bark itself; the human evidence comes from trials of berberine, and berberine carries real drug-interaction and newborn risks. Wild trees have been stripped to the point that the species is protected in China.

What it is used for

  • Diarrhoea
    Limited

    WHO lists use for abdominal pain, diarrhoea and gastroenteritis in pharmacopoeias but found no trials of the bark. In trials of berberine, its main alkaloid, it reduced stool volume in E. coli diarrhoea and modestly in cholera, where tetracycline worked better, and did no better than placebo in non-cholera diarrhoea. How far this applies to the bark is unknown.1

  • Honey-processed bark is used in Chinese practice for mouth ulcers. In a clinical trial in 152 people, a toothpaste containing 0.05% bark extract reduced gum inflammation and redness over 4 weeks.2

  • A bark extract (Nexrutine) was given for 1–2 months to men with prostate cancer before surgery or during radiotherapy in a study designed to test tolerance. It was well tolerated, and PSA fell in 81% of men (by 17% on average). This does not show it treats prostate disease.2

  • Listed for urinary tract infections in pharmacopoeias (WHO). The Chinese Pharmacopoeia uses it for painful, difficult urination from 'heat' and for urinary tract infection. No clinical trials of the bark.1,2

  • The Chinese Pharmacopoeia lists it for eczema, damp sores, itching and swellings. Untested in trials.2

  • WHO records traditional use for burns, skin wounds and sores.1

  • Liver health
    Traditional

    Jaundice is among its uses from the Shennong Bencao Jing onward, and WHO records traditional use for jaundice. Not clinically tested.1,2

  • Pain (general)
    Traditional

    The Ainu used the fruit as a painkiller.3

How it is prepared

dry extract / capsule

WHO lists the crude bark, dried extracts, fluid extracts and tinctures. In Chinese practice the bark, raw or processed with salt, honey or rice wine, is rarely used alone and is usually combined with other herbs.

WHO monograph (2009), citing the Chinese Pharmacopoeia: 3–10 g crude drug a day.

Amounts are as recorded by the named source, not a recommendation.

Safety

Pregnancy
Avoid
Breastfeeding
Avoid
Children
WHO: no information. A 2026 review notes that safety in children has not been systematically evaluated.

Interactions with medicines

  • ciclosporinMajorIn kidney-transplant patients, berberine 0.2 g three times daily raised ciclosporin trough levels by about 89%.
  • drugs metabolised by CYP3A4, CYP2D6 or CYP2C9 (e.g. warfarin, statins, calcium-channel blockers, many antidepressants)ModerateBerberine inhibits these enzymes, and a bark extract inhibited cytochrome P450 in the lab; blood levels of these drugs may change.
  • P-glycoprotein substrates (e.g. digoxin, fexofenadine)ModerateBerberine affects this drug transporter, which may alter absorption and elimination.
  • chemotherapy such as paclitaxelModerateBerberine up-regulated the multidrug-resistance pump in tumour cells, which may reduce drug retention (lab data).
Interaction checker →

Do not use if

  • Allergy to the plant
  • Pregnancy, and newborns: berberine crosses the placenta and has been reported to cause kernicterus in newborns when used near term
  • In Chinese medical theory, 'spleen-stomach deficiency' with poor appetite, loose stools and a cold abdomen, because the herb is cold in nature

Side effects

  • Berberine was well tolerated at 0.5 g a day (WHO)
  • In the prostate-cancer tolerance study of Nexrutine, two patients had transient grade 3 effects (low potassium, urinary incontinence); other effects were mild

Toxicity

Toxicity studies cover only up to 90 days in animals and 3 months in people; safety of longer use is not established. High doses caused mild kidney-tubule changes in animals.

In the healing traditions

  • Traditional Chinese Medicine

    Huang bai (黄柏)

    Bitter and cold, entering the kidney and bladder channels. Clears heat, dries dampness, purges fire, relieves 'bone-steaming' fever and resolves toxicity: for damp-heat dysentery, jaundice, vaginal discharge with itching, painful urination, night sweats, seminal emission, sores and eczema. Usually used in formulas, such as Zhibai Dihuang Wan; salt-, honey- or rice-wine-processed forms are used for different purposes.

    Shennong Bencao Jing; Lei Gong Pao Zhi Lun; Chinese Pharmacopoeia

  • Ainu traditional medicine

    Shikerebe-ni (sikerpe)

    The fruit was used as a painkiller.

Active compounds

berberine
yellow isoquinoline alkaloid, up to 4.75% of the bark; antibacterial and antisecretory; tested in diarrhoea, trachoma and leishmaniasis
palmatine, jatrorrhizine, magnoflorine, phellodendrine
other isoquinoline alkaloids of the bark
limonoids
with the alkaloids, deter termites and insects, which helps explain why paper dyed with the bark resists pests

History

Huang bai is recorded in the Shennong Bencao Jing, the earliest Chinese materia medica, for jaundice, haemorrhoids and dysentery. Across East Asia its yellow dye was used on paper for sutras, including the Diamond Sutra, because it kept insects away. In 1926 the Japanese chemist Yoshion Murakami and colleagues isolated berberine from the Japanese variety of the tree.

Sources

  1. 1.WHO monographs on selected medicinal plants, vol. 4 (2009): Cortex Phellodendron
  2. 2.An updated and comprehensive review of Phellodendri amurensis Cortex: ethnobotany, geographical distribution, phytochemistry, quality control, and pharmacology. Molecules 2026;31:1318
  3. 3.Wikipedia: Phellodendron amurense (names, Ainu use, sutra dye, invasiveness)

Reference, not prescription. Nothing here is medical advice. Herbs can interact with medicines and be dangerous in pregnancy; tell your doctor or pharmacist about anything you take.